Implanted pulse generators with reduced power consumption via signal strength/duration characteristics, and associated systems and methods

ABSTRACT

Implanted pulse generators with reduced power consumption via signal strength-duration characteristics, and associated systems and methods are disclosed. A representative method for treating a patient in accordance with the disclosed technology includes receiving an input corresponding to an available voltage for an implanted medical device and identifying a signal delivery parameter value of an electrical signal based on a correlation between values of the signal delivery parameter and signal deliver amplitudes. The signal deliver parameter can include at least one of pulse width or duty cycle. The method can further include delivering an electrical therapy signal to the patient at the identified signal delivery parameter value using a voltage within a margin of the available voltage.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional Application62/000,985, filed on May 20, 2014 and incorporated herein by reference.

TECHNICAL FIELD

The present technology is directed generally to implanted pulsegenerators with reduced power consumption, obtained via signalstrength/duration characteristics, and associated systems and methods.Particular embodiments use a strength/duration characteristics toimprove the delivery of electrical stimulation for patient therapy, asthe voltage available from an implanted power source decreases.

BACKGROUND

Neurological stimulators have been developed to treat pain, movementdisorders, functional disorders, spasticity, cancer, cardiac disorders,and various other medical conditions. Implantable neurologicalstimulation systems generally have an implantable signal generator andone or more leads that deliver electrical pulses to neurological tissueor muscle tissue. For example, several neurological stimulation systemsfor spinal cord stimulation (SCS) have cylindrical leads that include alead body with a circular cross-sectional shape and one or moreconductive rings (i.e., contacts) spaced apart from each other at thedistal end of the lead body. The conductive rings operate as individualelectrodes and, in many cases, the SCS leads are implantedpercutaneously through a needle inserted into the epidural space, withor without the assistance of a stylet.

Once implanted, the signal generator applies electrical pulses to theelectrodes, which in turn modify the function of the patient's nervoussystem, such as by altering the patient's responsiveness to sensorystimuli and/or altering the patient's motor-circuit output. In SCStherapy for the treatment of pain, the signal generator applieselectrical pulses to the spinal cord via the electrodes. In conventionalSCS therapy, electrical pulses are used to generate sensations (known asparesthesia) that mask or otherwise alter the patient's sensation ofpain. For example, in many cases, patients report paresthesia as atingling sensation that is perceived as less uncomfortable than theunderlying pain sensation.

In contrast to traditional or conventional (i.e., paresthesia-based)SCS, a form of paresthesia-free SCS has been developed that uses therapysignal parameters that treat the patient's sensation of pain withoutgenerating paresthesia or otherwise using paresthesia to mask thepatient's sensation of pain. One of several advantages ofparesthesia-free SCS therapy systems is that they eliminate the need foruncomfortable paresthesias, which many patients find objectionable.However, a challenge with paresthesia-free SCS therapy systems is thatthe signal may be delivered at frequencies, amplitudes, and/or pulsewidths that may use more power than conventional SCS systems. This inturn can deplete the battery of the implanted system at an acceleratedrate. Accordingly, a follow-on challenge with providing spinal cordstimulation via an implanted pulse generator is that, in at least somecases, it may be difficult to maintain an effective signal as the chargeavailable from the pulse generator battery decreases. One approach tothe challenge in the context of conventional systems is to increase thefrequency with which the pulse generator is charged, but this can beinconvenient for the patient. Another approach is to add signalconditioning hardware, for example, to boost the voltage provided by thebattery as the battery discharges. A drawback with this approach is thatit can be inefficient. Accordingly, there remains a need for effectiveand efficient therapy signal delivery, despite the decreasing voltageavailable from the battery or other power source of an implanted pulsegenerator during normal use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially schematic illustration of an implantable spinalcord modulation system positioned at the spine to deliver therapeuticsignals in accordance with several embodiments of the presenttechnology.

FIG. 1B is a partially schematic, cross-sectional illustration of apatient's spine, illustrating representative locations for implantedlead bodies in accordance with embodiments of the present technology.

FIG. 2 is a flow diagram illustrating a process for delivering atherapeutic electrical signal in accordance with a representativeembodiment of the present technology.

FIG. 3 is a graph illustrating a family of curves representing signalamplitude as a function of pulse width or duty cycle.

FIG. 4 is a flow diagram illustrating a process for establishing a pulsewidth/amplitude correlation in accordance with an embodiment of thepresent technology.

FIG. 5 is a flow diagram illustrating a process for delivering a therapysignal with a reduced available power source voltage in accordance withan embodiment of the present technology.

FIG. 6 graphically illustrates a process for updating signal amplitudeand pulse width in accordance with an embodiment of the presenttechnology.

DETAILED DESCRIPTION

The present technology is directed generally to delivering electricalsignals (also referred to herein as “therapy signals”) at reducedavailable voltage levels in implanted patient therapy systems, such asspinal cord stimulation (SCS) systems. For example, in one embodiment,the present technology includes reducing signal amplitude and increasingpulse width or duty cycle to maintain a target energy delivery rate.Because the technology can be employed in SCS systems that providetherapy (e.g., pain relief) without generating paresthesia, the patientcan continue to receive effective therapy without sensing the amplitudechange. Accordingly, the present technology can effectively increase thetime between battery charging events, thus addressing potentialinstances in which paresthesia-free therapy might otherwise deplete thepower available from an implanted battery faster than would aconventional, paresthesia-based device.

General aspects of the environments in which the disclosed technologyoperates are described below under heading 1.0 (“Overview”) withreference to FIGS. 1A and 1B. Particular embodiments of the technologyare described further under heading 2.0 (“Representative Embodiments”)with reference to FIGS. 2-6. While the present technology is beingdescribed in the environment of SCS, one of skill in the art wouldrecognize that one or more aspects of the present technology areapplicable to other, non-SCS implantable and/or external devices; e.g.,implantable or external neurostimulators for treatment of one or morepatient indications.

1.0 Overview

One example of a paresthesia-free SCS therapy system is a “highfrequency” SCS system. High frequency SCS systems can inhibit, reduce,and/or eliminate pain via waveforms with high frequency elements orcomponents (e.g., portions having high fundamental frequencies),generally with reduced or eliminated side effects. Such side effects caninclude unwanted paresthesia, unwanted motor stimulation or blocking,unwanted pain or discomfort, and/or interference with sensory functionsother than the targeted pain. In a representative embodiment, a patientmay receive high frequency therapeutic signals with at least a portionof the therapy signal at a frequency of from about 1.5 kHz to about 100kHz, or from about 1.5 kHz to about 50 kHz, or from about 3 kHz to about20 kHz, or from about 5 kHz to about 15 kHz, or at frequencies of about8 kHz, 9 kHz, or 10 kHz. These frequencies are significantly higher thanthe frequencies associated with conventional “low frequency” SCS, whichare generally below 1,200 Hz, and more commonly below 100 Hz.Accordingly, modulation at these and other representative frequencies(e.g., from about 1.5 kHz to about 100 kHz) is occasionally referred toherein as “high frequency stimulation,” “high frequency SCS,” and/or“high frequency modulation.” Further examples of paresthesia-free SCSsystems are described in U.S. Patent Publication Nos. 2009/0204173 and2010/0274314, as well as U.S. Provisional Application No. 61/901,255,the respective disclosures of which are herein incorporated by referencein their entirety.

FIG. 1A schematically illustrates a representative patient therapysystem 100 for providing relief from chronic pain and/or otherconditions, arranged relative to the general anatomy of a patient'sspinal column 191. The system 100 can include a signal generator 101(e.g., an implanted pulse generator or IPG), which may be implantedsubcutaneously within a patient 190 and coupled to one or more signaldelivery elements or devices 110. The signal delivery elements ordevices 110 may be implanted within the patient 190, typically at ornear the patient's spinal cord midline 189. The signal delivery elements110 carry features for delivering therapy to the patient 190 afterimplantation. The signal generator 101 can be connected directly to thesignal delivery devices 110, or it can be coupled to the signal deliverydevices 110 via a signal link or lead extension 102. In a furtherrepresentative embodiment, the signal delivery devices 110 can includeone or more elongated lead(s) or lead body or bodies 111 (identifiedindividually as a first lead 111 a and a second lead 111 b). As usedherein, the terms signal delivery device, lead, and/or lead body includeany of a number of suitable substrates and/or support members that carryelectrodes/devices for providing therapy signals to the patient 190. Forexample, the lead or leads 111 can include one or more electrodes orelectrical contacts that direct electrical signals into the patient'stissue, e.g., to provide for therapeutic relief. In other embodiments,the signal delivery elements 110 can include structures other than alead body (e.g., a paddle) that also direct electrical signals and/orother types of signals to the patient 190.

In a representative embodiment, one signal delivery device may beimplanted on one side of the spinal cord midline 189, and a secondsignal delivery device may be implanted on the other side of the spinalcord midline 189. For example, the first and second leads 111 a, 111 bshown in FIG. 1A may be positioned just off the spinal cord midline 189(e.g., about 1 mm offset) in opposing lateral directions so that the twoleads 111 a, 111 b are spaced apart from each other by about 2 mm. Inparticular embodiments, the leads 111 may be implanted at a vertebrallevel ranging from, for example, about T8 to about T12. In otherembodiments, one or more signal delivery devices can be implanted atother vertebral levels, e.g., as disclosed in U.S. Patent ApplicationPublication No. 2013/0066411, and incorporated herein by reference inits entirety.

The signal generator 101 can transmit signals (e.g., electrical signals)to the signal delivery elements 110 that up-regulate (e.g., excite)and/or down-regulate (e.g., block or suppress) target nerves. As usedherein, and unless otherwise noted, the terms “modulate,” “modulation,”“stimulate,” and “stimulation” refer generally to signals that haveeither type of the foregoing effects on the target nerves. The signalgenerator 101 can include a machine-readable (e.g., computer-readable)medium containing instructions for generating and transmitting suitabletherapy signals. The signal generator 101 and/or other elements of thesystem 100 can include one or more processor(s) 107, memory unit(s) 108,and/or input/output device(s) 112. Accordingly, the process of providingmodulation signals, providing guidance information for positioning thesignal delivery devices 110, and/or executing other associated functionscan be performed by computer-executable instructions contained by, on orin computer-readable media located at the pulse generator 101 and/orother system components. Further, the pulse generator 101 and/or othersystem components may include dedicated hardware, firmware, and/orsoftware for executing computer-executable instructions that, whenexecuted, perform any one or more methods, processes, and/orsub-processes described herein; e.g., the methods, processes, and/orsub-processes described with reference to FIGS. 2-6 below. Saiddedicated hardware, firmware, and/or software also serve as “means for”performing the methods, processes, and/or sub-processes describedherein. The signal generator 101 can also include multiple portions,elements, and/or subsystems (e.g., for directing signals in accordancewith multiple signal delivery parameters), carried in a single housing,as shown in FIG. 1A, or in multiple housings.

The signal generator 101 can also receive and respond to an input signalreceived from one or more sources. The input signals can direct orinfluence the manner in which the therapy and/or process instructionsare selected, executed, updated, and/or otherwise performed. The inputsignals can be received from one or more sensors (e.g., an input device112 shown schematically in FIG. 1 for purposes of illustration) that arecarried by the signal generator 101 and/or distributed outside thesignal generator 101 (e.g., at other patient locations) while stillcommunicating with the signal generator 101. The sensors and/or otherinput devices 112 can provide inputs that depend on or reflect patientstate (e.g., patient position, patient posture, and/or patient activitylevel), and/or inputs that are patient-independent (e.g., time). Stillfurther details are included in U.S. Pat. No. 8,355,797, incorporatedherein by reference in its entirety.

In some embodiments, the signal generator 101 and/or signal deliverydevices 110 can obtain power to generate the therapy signals from anexternal power source 103. In one embodiment, for example, the externalpower source 103 can by-pass an implanted signal generator and generatea therapy signal directly at the signal delivery devices 110 (or viasignal relay components). The external power source 103 can transmitpower to the implanted signal generator 101 and/or directly to thesignal delivery devices 110 using electromagnetic induction (e.g., RFsignals). For example, the external power source 103 can include anexternal coil 104 that communicates with a corresponding internal coil(not shown) within the implantable signal generator 101, signal deliverydevices 110, and/or a power relay component (not shown). The externalpower source 103 can be portable for ease of use.

In another embodiment, the signal generator 101 can obtain the power togenerate therapy signals from an internal power source, in addition toor in lieu of the external power source 103. For example, the implantedsignal generator 101 can include a non-rechargeable battery or arechargeable battery to provide such power. When the internal powersource includes a rechargeable battery, the external power source 103can be used to recharge the battery. The external power source 103 canin turn be recharged from a suitable power source (e.g., conventionalwall power).

During at least some procedures, an external stimulator or trialmodulator 105 can be coupled to the signal delivery elements 110 duringan initial procedure, prior to implanting the signal generator 101. Forexample, a practitioner (e.g., a physician and/or a companyrepresentative) can use the trial modulator 105 to vary the modulationparameters provided to the signal delivery elements 110 in real time,and select optimal or particularly efficacious parameters. Theseparameters can include the location from which the electrical signalsare emitted, as well as the characteristics of the electrical signalsprovided to the signal delivery devices 110. In some embodiments, inputis collected via the external stimulator or trial modulator and can beused by the clinician to help determine what parameters to vary. In atypical process, the practitioner uses a cable assembly 120 totemporarily connect the trial modulator 105 to the signal deliverydevice 110. The practitioner can test the efficacy of the signaldelivery devices 110 in an initial position. The practitioner can thendisconnect the cable assembly 120 (e.g., at a connector 122), repositionthe signal delivery devices 110, and reapply the electrical signals.This process can be performed iteratively until the practitioner obtainsthe desired position for the signal delivery devices 110. Optionally,the practitioner may move the partially implanted signal deliverydevices 110 without disconnecting the cable assembly 120. Furthermore,in some embodiments, the iterative process of repositioning the signaldelivery devices 110 and/or varying the therapy parameters may not beperformed.

The signal generator 101, the lead extension 102, the trial modulator105 and/or the connector 122 can each include a receiving element 109.Accordingly, the receiving elements 109 can be patient implantableelements, or the receiving elements 109 can be integral with an externalpatient treatment element, device or component (e.g., the trialmodulator 105 and/or the connector 122). The receiving elements 109 canbe configured to facilitate a simple coupling and decoupling procedurebetween the signal delivery devices 110, the lead extension 102, thepulse generator 101, the trial modulator 105 and/or the connector 122.The receiving elements 109 can be at least generally similar instructure and function to those described in U.S. Patent ApplicationPublication No. 2011/0071593, incorporated by reference herein in itsentirety.

After the signal delivery elements 110 are implanted, the patient 190can receive therapy via signals generated by the trial modulator 105,generally for a limited period of time. During this time, the patientwears the cable assembly 120 and the trial modulator 105 outside thebody. Assuming the trial therapy is effective or shows the promise ofbeing effective, the practitioner then replaces the trial modulator 105with the implanted signal generator 101, and programs the signalgenerator 101 with therapy programs selected based on the experiencegained during the trial period. Optionally, the practitioner can alsoreplace the signal delivery elements 110. Once the implantable signalgenerator 101 has been positioned within the patient 190, the therapyprograms provided by the signal generator 101 can still be updatedremotely via a wireless physician's programmer (e.g., a physician'slaptop, a physician's remote or remote device, etc.) 117 and/or awireless patient programmer 106 (e.g., a patient's laptop, patient'sremote or remote device, etc.). Generally, the patient 190 has controlover fewer parameters than does the practitioner. For example, thecapability of the patient programmer 106 may be limited to startingand/or stopping the signal generator 101, and/or adjusting the signalamplitude. The patient programmer 106 may be configured to accept painrelief input as well as other variables, such as medication use.

In any of the foregoing embodiments, the parameters in accordance withwhich the signal generator 101 provides signals can be adjusted duringportions of the therapy regimen. For example, the frequency, amplitude,pulse width, and/or signal delivery location can be adjusted inaccordance with a pre-set therapy program, patient and/or physicianinputs, and/or in a random or pseudorandom manner. Such parametervariations can be used to address a number of potential clinicalsituations. Certain aspects of the foregoing systems and methods may besimplified or eliminated in particular embodiments of the presentdisclosure. Further aspects of these and other expected beneficialresults are detailed in U.S. Patent Application Publication Nos.2010/0274317; 2010/0274314; 2009/0204173; and 2013/0066411, each ofwhich is incorporated herein by reference in its entirety.

FIG. 1B is a cross-sectional illustration of the spinal cord 191 and anadjacent vertebra 195 (based generally on information from Crossman andNeary, “Neuroanatomy,” 1995 (published by Churchill Livingstone)), alongwith multiple leads 111 (shown as leads 111 a-111 e) implanted atrepresentative locations. For purposes of illustration, multiple leads111 are shown in FIG. 1B implanted in a single patient. In actual use,any given patient will likely receive fewer than all the leads 111 shownin FIG. 1B.

The spinal cord 191 is situated within a vertebral foramen 188, betweena ventrally located ventral body 196 and a dorsally located transverseprocess 198 and spinous process 197. Arrows V and D identify the ventraland dorsal directions, respectively. The spinal cord 191 itself islocated within the dura mater 199, which also surrounds portions of thenerves exiting the spinal cord 191, including the ventral roots 192,dorsal roots 193 and dorsal root ganglia 194. The dorsal roots 193 enterthe spinal cord 191 at the dorsal root entry zone 187, and communicatewith dorsal horn neurons located at the dorsal horn 186. In oneembodiment, the first and second leads 111 a, 111 b are positioned justoff the spinal cord midline 189 (e.g., about 1 mm. offset) in opposinglateral directions so that the two leads 111 a, 111 b are spaced apartfrom each other by about 2 mm, as discussed above. In other embodiments,a lead or pairs of leads can be positioned at other locations, e.g.,toward the outer edge of the dorsal root entry zone 187 as shown by athird lead 111 c, or at the dorsal root ganglia 194, as shown by afourth lead 111 d, or approximately at the spinal cord midline 189, asshown by a fifth lead 111 e.

2.0 Representative Embodiments

As discussed above, systems of the type described with reference toFIGS. 1A-B can include implanted pulse generators having rechargeablebatteries or other rechargeable power sources that are periodicallyrecharged with an external recharger. As the battery discharges, thevoltage put out by the battery typically also decreases. Conventionaltechniques for addressing this voltage reduction (and voltage variationgenerally) include “boost and buck” devices. However, a drawback withsuch devices is that they are inefficient. In particular, such devicescan reduce the overall efficiency of delivering electrical signals tothe patient by 20%-30%.

FIG. 2 illustrates a process 200 for more efficiently providing powerfrom an implanted battery (or other power source), as the batterydischarges. The process can make use of the relationship between thepulse width and amplitude for therapy signals applied to a patient.Accordingly, the process 200 can include establishing a pulsewidth/amplitude correlation, e.g., on a patient-by-patient basis (block202). The process 200 can further include receiving a request for atherapy amplitude (block 204). The request may come via a patient orpractitioner selecting a particular therapy program, and/or requestingan amplitude adjustment once the particular program has been activated.The amplitude can be a current amplitude (e.g., in the context of asystem that includes a current source between the power source and theelectrodes), or a voltage amplitude. In block 206, the available voltageis measured or otherwise identified (e.g., at the battery, or downstreamfrom the battery). The method further includes setting the pulse widthto provide the requested therapy amplitude based on the availablevoltage and the pulse width/amplitude correlation (block 208).Accordingly, the pulse width can be adjusted to provide the same orapproximately the same level of therapy to the patient despite the factthat the available voltage (e.g., the battery output voltage) hasdecreased.

FIG. 3 illustrates a graph 300 of signal amplitude as a function ofpulse width or duty cycle. For much of the discussion that follows, thefunctions will be described in the context of amplitude as a function ofpulse width, with the understanding that the function and therelationships associated with the function may apply to duty cycle aswell.

FIG. 3 illustrates a plurality of curves 302 (four are shown asfirst-fourth curves 302 a-302 d) that indicate the functionalrelationship between amplitude and pulse width for a variety ofdifferent patients, evaluation criteria, and/or other factors. Thesecurves are often referred to as “strength-duration” curves. Each curve302 represents amplitude as a function of pulse width for an effectiveor target level of electrical stimulation. For example, an effectivelevel of stimulation can include a level of stimulation that providespain relief without paresthesia. In another embodiment, a target levelof stimulation can include stimulation sufficient to generate a sensoryresponse (e.g., paresthesia or another sensation) in the patient. For agiven patient, the curve may differ depending upon whether the targetresult is paresthesia-free therapy, or a sensory response. In addition,the curve for an effective or target stimulation level may be differentfor one patient than for another. Accordingly, there can exist multiplecurves (as shown in FIG. 3) that may be patient-specific and/or targetlevel-specific.

As is also shown in FIG. 3, the pulse width or duty cycle can vary as afunction of the available voltage, in a manner similar to the manner inwhich these parameters vary with amplitude. In particular, each curve302 can indicate the pulse width or duty cycle appropriate for a givenavailable voltage, assuming a fixed impedance for the signal deliverycircuit. Accordingly, FIG. 3 indicates that a given therapy level orefficacy can be delivered with a relatively high voltage and short pulsewidth, or with a lower voltage and longer pulse width. The relationshipsbetween amplitude, available voltage, and pulse width or duty cycleshown in FIG. 3 are used to implement the methods discussed furtherbelow with reference to FIGS. 4-6.

FIG. 4 illustrates representative processes for establishing anamplitude/pulse width correlation, as described above with reference toblock 202 in FIG. 2. The process 202 can include establishing a “map”with a series of pulse width/amplitude curves (block 404). The map canhave the format shown in FIG. 3 in some embodiments, and in otherembodiments, the map can have other formats. Such formats can includeother graphical formats, a tabular format, a series of equationsdescribing individual curves or functions, and/or other suitabletechniques for establishing a correlation between amplitude and pulsewidth. The map can be based on clinical data obtained from multiplepatients. In particular embodiments, different maps can be establishedfor different parameters (e.g., different patient indications, patientphysiologies and/or treatment parameters).

In block 406, the process includes identifying the values (e.g.,numerical values) for one or more patient-specific pulse width/amplitudepairs or coordinates. For example, referring to FIG. 3, the practitionercan identify a single point 310 a based on data received from thepatient, which is sufficient to indicate that the appropriatepatient-specific curve is the first curve 302 a. The data may indicatethat the patient receives effective therapy at the amplitude and pulsewidth coordinates of the first point 310 a. Another patient may becharacterized by a second point 310 b and accordingly have the secondcurve 302 b as his/her patient-specific curve. Still another patient maybe characterized by a third point 310 c and accordingly have the thirdcurve 302 c as his/her patient-specific curve.

In another embodiment, an individual patient may have a plurality ofpoints associated with him or her, e.g., first-sixth points 310 a-310 f.In this particular instance, four of the six points (points 310 b, 310d, 310 e, 310 f) fall on the second curve 302 b, which can be asufficient indication that the particular patient's patient-specificcurve is the second curve 302 b.

In still further embodiments, different points can correspond to adifferent parameter for the same individual patient. For example, thefirst point 310 a (and the associated first curve 302 a) can correspondto a level of paresthesia-free therapy at a particular vertebral level.The second point 310 b (and the associated second curve 302 b) cancorrespond to a stimulation threshold, for example, the threshold atwhich the patient first feels paresthesia or another sensation. Thethird point 310 c (and the associated third curve 302 c) can correspondto the threshold at which a signal applied to the patient produces anevoked potential. The evoked potential can be physically measured, thusindicating at which amplitude and pulse width the patient's neuronsgenerate an action potential in response to a stimulus at theamplitude/pulse width coordinates of the third point 310 c. Methods forestablishing which of the curves shown in FIG. 3 is an appropriatepatient-specific curve are further described below, with reference tothe three thresholds described above: the paresthesia or sensorythreshold, the therapeutic threshold, and the evoked potentialthreshold.

Returning to FIG. 4, in block 408, the process includes identifying thepatient-specific correlation using paresthesia. This process can includeselecting an amplitude (block 414), selecting a pulse width (block 416),and administering a signal to the patient in accordance with theselected amplitude and pulse width (block 418). In at least someinstances, the pulse width and/or amplitude used for this process may bedeliberately selected to be different than the expected pulse widthand/or amplitude used for therapy. In particular, the selected amplitudeand/or pulse width can be more likely to produce paresthesia. Block 419includes determining whether the patient reports paresthesia or anothersuitable sensory feedback. If not, the amplitude is increased at block420 and the signal is re-administered. Once the patient reportsparesthesia, block 422 includes determining whether another coordinatepair (e.g., another pair of amplitude and pulse width values) is to beobtained. If so, the process returns to block 414. If not, the processproceeds to block 424 where it is determined whether or not to apply acorrection factor to the coordinate pair or pairs obtained in block 422.

The correction factor can be based on any of a number of suitableparameters. For example, a representative correction factor can includereducing the reported amplitude to account for the expected amplitudedifference between a signal that produces paresthesia and a signal thatcan produce therapy (e.g., pain relief) without paresthesia. If thepulse width used to generate paresthesia is different than the expectedtherapeutic pulse width, the correction factor can also account for thatdifference. In any of these embodiments, the correction factor can bepatient-specific, or it can be determined from a pool of patient data.The correction factor can be determined empirically through patienttesting, or it can be estimated and/or calculated, depending upon theparticular embodiment. If such a correction factor is to be applied, itis applied in block 428.

The process then proceeds to block 426 where the coordinate orcoordinates, with or without a correction factor, are used to identifythe patient-specific curve on the map established at block 404. Forexample, with reference again to FIG. 3, the coordinates can be used todetermine which of the multiple curves 302 best corresponds to or fitswith the coordinate or coordinates obtained in block 422. Once theappropriate curve is identified, the curve can be used to selecttherapeutic amplitudes and pulse widths as a function of availablevoltage, in a manner described later with reference to FIGS. 5 and 6.

As noted above, block 408 includes identifying the patient-specificcurve (or other correlation) in conjunction with a paresthesia thresholdidentified by the patient. Other techniques can be used to establishwhich correlation is best suited to an individual patient. For example,block 410 includes identifying the patient-specific correlation based onthe threshold at which the patient receives or experiencesparesthesia-free pain relief. In this process, the amplitude and pulsewidth are selected (blocks 430 and 432) and the signal is administeredto the patient (block 434). Instead of identifying whether or not thepatient has paresthesia, as discussed above with reference to block 419,block 436 can include determining whether the patient has receivedtherapy (e.g., pain relief) without paresthesia. If not, the amplitudeis increased in block 437 and the signal is re-administered to thepatient. If therapy without paresthesia is obtained, block 438 includesdetermining whether to obtain an additional coordinate pair. If not, theprocess proceeds to block 424 to determine whether a correction factoris to be applied and, with or without the correction factor, block 426includes identifying the patient-specific curve or correlation using themap established in block 404.

In at least some embodiments, it is expected that it may take some timefor the patient to detect and report the paresthesia-free therapy (e.g.,pain relief). In such instances, it may be more efficient to use theparesthesia threshold technique described above with reference to blocks408-422 (e.g., with a correction factor applied), or to use othertechniques that can more rapidly identify the amplitude/pulse widthcoordinates. One such technique includes identifying thepatient-specific curve or correlation via an evoked potential (block412). This process also includes selecting an amplitude (block 440),selecting a pulse width (block 442), and applying a therapy signal withthe selected amplitude and pulse width (block 444). In block 446, theprocess includes checking for an evoked potential (e.g., a physiologicalelectrical response to a stimulation signal at the selected amplitudeand pulse width). If no evoked potential is measured, then in block 447the amplitude is increased and the signal is re-administered to thepatient in block 444. If an evoked potential is measured, then block 448includes determining whether or not to obtain an additionalamplitude/pulse width coordinate pair. The process then proceeds toblock 424 (determining whether or not to apply a correction factor) andto block 426 to identify the patient-specific correlation or curve onthe map established in block 404.

The result of any of the foregoing embodiments described above withreference FIG. 4 is identifying a patient-specific curve or correlationbetween signal amplitude and pulse width (or duty cycle). FIG. 5illustrates a representative process 500 for using this information toidentify a therapeutic amplitude and pulse width as a function of avariable available voltage (e.g., battery output voltage or a downstreamcorrelate of battery output voltage). In block 502, the patient orpractitioner selects a requested therapy amplitude, which is received bythe system at block 504. In block 506, the system receives an initialpulse width and frequency. In at least some embodiments, the initialpulse width and frequency are established by default values stored inmemory so that neither the patient nor the practitioner needs toseparately input these values. In other embodiments, one or both ofthese values can be selected by the patient or practitioner. In any ofthese embodiments, block 508 includes temporarily setting the availablevoltage high enough to generate a signal at any selected amplitude(within a proscribed limit). This may include using a boost circuit ifthe battery voltage is insufficient. However, even if a boost circuit isused for this portion of the process, it need not be used to generatethe therapy signal over a long period of time, which, as discussed abovecan produce system efficiencies.

In block 510, one or more pulses are delivered at the requestedamplitude, with the initial pulse width and the initial frequency. Asthe pulses are delivered, the voltage across the therapy circuit ismeasured or otherwise determined (block 512). For example, if the signalis delivered to a bipole (two electrodes), the voltage across the bipoleis measured. In block 514, the voltage required to deliver a consistenttherapy signal at the requested amplitude, and with the initial pulsewidth and frequency, is determined. This process can include adding amargin (e.g., a loss margin and/or an impedance variation margin) to thetherapy circuit voltage measured at block 512. Typical margins rangefrom 100 mV to 1.5V. Accordingly, block 514 can account for one or moresystem losses, variations, and/or measurement inaccuracies. In block516, the available voltage is measured. The available voltage can bedetermined (e.g., measured) at the battery or at any other suitablepoint (e.g., downstream point) at which the voltage is at leastcorrelated with the available battery voltage. In block 518, therequired voltage is compared to the available voltage. If the requiredvoltage does not exceed the available voltage, then the requestedtherapy signal is delivered at block 520. If the required voltageexceeds the available voltage, then the process continues at block 522.

In block 522, the process includes determining the circuit impedance(e.g., the impedance of the circuit that provides therapy to thepatient, including the signal delivery electrodes and the patient's owntissue). The impedance can be obtained using voltage/current/impedancerelationships (e.g., V=IR) based on the requested current amplitude(from block 504) and the measured therapy circuit voltage (from block512). In block 524, the process includes calculating an updated currentamplitude based on the available voltage and circuit impedance. Blocks522 and 524 are typically implemented for a current-based system, e.g.,a system with a current source connected between the battery or otherpower source and the electrodes. Accordingly, these blocks may beskipped or deleted in a voltage-amplitude-based system.

Blocks 526 and 528 are discussed below with reference to FIG. 6. Block526 includes determining an updated pulse width from the identifiedpatient-specific curve. FIG. 6 illustrates a representativepatient-specific curve 302 b with the requested amplitude 610 a andinitial pulse width 610 b identified as an initial therapy point 610.The updated amplitude 620 a identified in block 524 is also indicated inFIG. 6. By proceeding along the patient-specific curve 302 b asindicated by arrow A1, the program can identify an updated coordinatepair 620 having the updated amplitude 620 a and a corresponding updatedpulse width 620 b. The therapy signal to be applied to the patient willbe applied with the updated amplitude 620 a and the updated pulse width620 b.

Block 528 determines, if necessary, an updated frequency. For example,if the updated pulse width is significantly greater than the initialpulse width, then the frequency may need to be decreased to account forthe change. Alternatively, if an interpulse interval (e.g., the timeperiod between adjacent pulses) is long enough to allow for an increasein pulse width without requiring a decrease in frequency, then thefrequency can remain the same. In either case, a therapy signal with theupdated amplitude, the updated pulse width, and the initial (or updated)frequency is then delivered at block 520.

The foregoing processes can be invoked, as needed, during the normalcourse of therapy. For example, the process described above withreference to FIG. 4 may be completed when the patient first beginsreceiving the therapy, and need not be repeated unless, for example,there is a basis for believing that the patient-specific correlationbetween pulse width and amplitude has shifted. The process describedabove with reference to FIG. 5 can be invoked periodically throughoutthe normal course of therapy. In another embodiment, the processdescribed above with reference to FIG. 5 can first be invoked when thebattery voltage (or other measure of available voltage) falls below athreshold level, and can then be invoked periodically until the batteryis recharged. For current-based systems, it may be beneficial todetermine the circuit impedance (block 522 in FIG. 5) relativelyfrequently to account for factors such as scar tissue build-up that mayaffect impedance.

One feature of at least some of the foregoing embodiments is that theycan include using an established relationship between amplitude andpulse width (or duty cycle) to produce therapeutic results even when thevoltage of the battery providing power for the electrical signal isreduced. An advantage of this arrangement is that it can eliminate theneed for a boost circuit to deliver therapy, except as may be needed toidentify the therapy delivery parameters. A corresponding advantage ofthis feature is that, because boost circuits can be inefficient, theamount of power lost as a result of delivering a therapy signal with areduced battery output voltage can be reduced. Accordingly, the batterycan last longer and can increase the time between battery chargingevents.

Another feature of at least some of the foregoing embodiments describedabove is that they may have particular applicability to therapies thatdo not produce paresthesia or other sensations in the patient. Inparticular, therapies that produce (and more generally rely on)paresthesia or other sensations may have those paresthesias orsensations change in nature, strength, and/or duration if the amplitudeis shifted in the manner described above. Because it is expected thatthe amplitude for paresthesia-free therapy may be shifted without beingsensed or detected by the patient, the foregoing process may beparticularly beneficial in the context of therapies that do not produceparesthesia.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the disclosed technology. For example,embodiments described above in the context of pulse width as a functionof amplitude can apply as well for duty cycle as a function ofamplitude. While the foregoing embodiments were described in the contextof battery voltage and an associated current amplitude produced by anintermediate current source, in other embodiments, the technique can beapplied in a voltage-amplitude-based system. In such embodiments, theamplitude axis of the curves shown in FIGS. 3 and 6 is voltageamplitude, and the pulse width can be determined directly from the curve(using the determined available voltage) without the intermediate stepof calculating an updated amplitude based on the available voltage andcircuit impedance.

In particular embodiments, representative current amplitudes for thetherapy signal are from 0.1 mA to 20 mA, or 0.5 mA to 10 mA, or 0.5 mAto 7 mA, or 0.5 mA to 5 mA. Representative pulse widths range from about10 microseconds to about 333 microseconds, about 10 microseconds toabout 166 microseconds, 20 microseconds to about 100 microseconds, 30microseconds to about 100 microseconds, and 30 microseconds to about 40microseconds. Duty cycles can range from about 10% to about 100%, and ina particular duty cycle, signals are delivered for 20 seconds andinterrupted for 2 minutes (an approximate 14% duty cycle). In otherembodiments, these parameters can have other suitable values. Forexample, in at least some embodiments, the foregoing systems and methodsmay be applied to therapies that have frequencies outside the rangesdiscussed above (e.g., 1.5 kHz-100 kHz) but which also do not produceparesthesia. Representative therapies include therapies havingrelatively narrow pulse widths, as disclosed in co-pending U.S.Provisional Patent Application No. 61/901,255, filed Nov. 7, 2013 andincorporated herein by reference. Representative pulse widths (which canbe delivered at frequencies above or below 1.5 kHz, depending upon theembodiment) include pulse widths from 10-50 microseconds, 20-40microseconds, 25-35 microseconds, 30-35 microseconds, and 30microseconds.

In still further embodiments, techniques generally similar to thosedescribed above may be applied to therapies that are directed to tissuesother than the spinal cord. Representative tissues can includeperipheral nerve tissue and/or brain tissue. In such contexts, thestrength/duration relationships discussed above can be the same as ordifferent than the relationships for spinal cord neurons, depending onthe embodiment. The mechanism of action by which pain relief is obtainedin any of the foregoing embodiments may include, but is not limited to,those described in co-pending U.S. Provisional Patent Application No.61/833,392, filed Jun. 10, 2013 and incorporated herein by reference.

In other embodiments, other methodologies may be used to provide paintherapy to the patient, and in some instances, such methodologies mayprovide paresthesia-free pain relief. Representative methods asserted toprovide paresthesia-free pain relief are disclosed in U.S. Pat. No.8,224,453 to De Ridder and U.S. Pat. No. 8,380,318 to Kishawi et al. DeRidder discloses the use of “burst” stimulation (e.g., bursts of spikesat a frequency of up to 1,000 Hz, with a 0.1-1.0 millisecond intervalbetween spikes, and a quiescent period of 1 millisecond to about 5seconds between bursts) applied to the spinal cord. Kishawi et al.discloses applying a signal to the dorsal root ganglion at a frequencyof less than 25 Hz, a pulse width of less than 120 microseconds and anamplitude of less than 500 microamps.

In several embodiments described above, a patient-specific relationshipincludes determining the amplitude and pulse width based onpatient-specific testing. In other embodiments, where applicable, datafrom a pool of patients (e.g., patients with the same pain indicationand/or other attributes) can be applied to a similarly situated patientwithout the need for a patient-specific test. Several embodiments weredescribed above in the context of a battery (e.g., a lithium ionbattery), and in other embodiments, the technology is applicable toother rechargeable power sources, e.g., capacitors.

Certain aspects of the technology described in the context of particularembodiments may be combined or eliminated in other embodiments. Forexample, selected process steps may be combined in some embodiments, andskipped in others. In particular embodiments, specific values describedabove (e.g., battery voltage, signal amplitude and the like) may bereplaced by correlates of these values for data handling or otherpurposes. Certain of the processes described above may be carried out inan automated or semi-automated manner using the implanted signalgenerator 101 described above with reference to FIG. 1A. In otherembodiments, some of the foregoing steps may be carried out by anexternal device (e.g., the physician programmer 117).

3.0 Additional Embodiments

In one embodiment, there is provide a method for treating a patient,comprising: receiving an input corresponding to an available voltage foran implanted medical device; identifying a signal delivery parametervalue of an electrical signal based on a correlation between values ofthe signal delivery parameter and signal delivery amplitudes, whereinthe signal delivery parameter includes at least one of pulse width orduty cycle; and delivering an electrical therapy signal to the patientat the identified signal delivery parameter value using a voltage withina margin of the available voltage. The signal delivery parameter may bepulse width and/or duty cycle. The available voltage may be an outputvoltage of a battery that provides power for the electrical therapysignal. The method may further comprise: receiving at least one inputcorresponding to a target therapy amplitude and a target pulse width;determining that the available voltage is insufficient to supply atherapy signal at the target therapy amplitude and the target pulsewidth; identifying an updated therapy amplitude less than the targettherapy amplitude; based at least in part on the updated therapyamplitude and the correlation, identifying an updated pulse widthgreater than the target pulse width; and delivering the electricaltherapy signal to the patient at the updated therapy amplitude and theupdated pulse width. The correlation may be patient-specificcorrelation, and wherein the method may further comprise establishingthe correlation. Establishing the correlation may include establishingthe correlation by producing paresthesia in the patient, and whereindelivering the electrical therapy signal does not produce paresthesia inthe patient.

In another embodiment, there is provided a method for treating pain in apatient, comprising: establishing a patient-specific correlation betweenamplitudes and pulse widths by identifying at least one pulsewidth/amplitude pair that produces a detectable result in the patient;receiving at least one input corresponding to a target therapyamplitude, pulse width and frequency; determining an available voltageof a battery-powered implanted medical device; determining whether theavailable voltage is sufficient to direct a therapy signal to thepatient at the target therapy amplitude, pulse width and frequency; andif the available voltage is not sufficient: determining an updatedtherapy amplitude and, based on the patient-specific correlation, anupdated pulse width; and delivering an electrical therapy signal to thepatient at the updated therapy amplitude and the updated pulse width;and if the available voltage is sufficient: delivering an electricaltherapy signal to the patient at the target amplitude and pulse width.The detectable result may be a non-therapeutic result, and wherein themethod may further comprise applying a correction factor to thepatient-specific correlation to account for an expected differencebetween the non-therapeutic result and a target therapeutic result. Thenon-therapeutic result may include producing paresthesia in the patientand wherein the target therapeutic result may include producing painrelief without paresthesia in the patient. The method may furthercomprise determining if the updated pulse width can be delivered at thetarget frequency; and if the updated pulse width cannot be delivered atthe target frequency, updating the target frequency. Establishing thepatient-specific correlation may include using the at least one pulsewidth/amplitude pair to determine which of a plurality of pulsewidth/amplitude correlations applies to the patient. At least one pulsewidth/amplitude pair may be one of multiple pulse width/amplitude pairsused to determine which of the plurality of pulse width/amplitudecorrelations applies to the patient. Establishing the patient-specificcorrelation may include using data from other patients. Identifying theat least one pulse width/amplitude pair may be based at least in part onproducing paresthesia in the patient with a signal having the pulsewidth and amplitude of the at least one pulse width/amplitude pair.Identifying the at least one pulse width/amplitude pair may be based atleast in part on producing pain relief without producing paresthesia inthe patient, with a signal having the pulse width and amplitude of theat least one pulse width/amplitude pair. Identifying the at least onepulse width/amplitude pair may be based at least in part on producing anevoked potential in the patient with a signal having the pulse width andamplitude of the at least one pulse width/amplitude pair. Determiningthe updated therapy amplitude may be based at least in part on theavailable voltage and on an impedance of a circuit via which theelectrical therapy signal is delivered. The method may further comprisedetermining the impedance by: delivering an electrical therapy signal atthe target amplitude and pulse width; determining a voltage across thecircuit; and determining the impedance based on the target amplitude andthe voltage across the circuit.

In another embodiment, there is provided a method of treating a patientby programming an implantable/external pulse generator to perform anyone or more of the herein described methods, process, and/orsub-processes. In still another embodiment, there is provided a systemfor treating a patient comprising means for performing any one or moreof the herein described methods, process, and/or sub-processes.

In another embodiment, there is provided a patient therapy system,comprising: (a) a pulse generator programmed with instructions fordelivering an electrical therapy signal to a patient; (b) a processoroperatively coupled to the pulse generator and programmed withinstructions that, when executed: receive an input corresponding to anavailable voltage for the pulse generator; identify a signal deliveryparameter value of an electrical signal based on a correlation betweenvalues of the signal delivery parameter and signal delivery amplitudes,wherein the signal delivery parameter includes at least one of pulsewidth or duty cycle; and direct the pulse generator to deliver anelectrical therapy signal at the identified signal delivery parametervalue using a voltage within a margin of the available voltage. Thesystem may further comprise a signal delivery element coupled to thepulse generator to deliver the electrical therapy signal to a patient.The processor and the pulse generator may be housed in apatient-implantable device. The pulse generator may be housed in apatient-implantable device, and the processor may be housed in anexternal device. The system may further comprise a computer-readablemedium coupled to the processor, and wherein the instructions arecarried by the computer-readable medium. The pulse generator may beprogrammed with instructions for delivering the electrical therapysignal at a frequency of from 1.5 kHz to 100 kHz (or any range of theabove-described frequencies). The pulse generator may be programmed withinstructions for delivering the electrical therapy signal at a pulsewidth of from 10 microseconds to 333 microseconds (or any range of theabove-described pulse widths). The processor may be programmed withinstructions that, when executed: receive at least one inputcorresponding to a target therapy amplitude and a target pulse width;determine that the available voltage is insufficient to supply a therapysignal at the target therapy amplitude and the target pulse width;identify an updated therapy amplitude less than the target therapyamplitude; based at least in part on the updated therapy amplitude andthe correlation, identify an updated pulse width greater than the targetpulse width; and deliver the electrical therapy signal to the patient atthe updated therapy amplitude and the updated pulse width.

In yet another embodiment, there is provide a patient therapy system,comprising: (a) an implantable housing; (b) a pulse generator carriedwithin the housing and programmed with instructions for delivering anelectrical therapy signal to a patient; (c) an implantable signaldelivery element coupled to the pulse generator; (d) a battery carriedwithin the housing and coupled to the pulse generator to provide powerfor the electrical therapy signal; and (e) a processor carried withinthe housing and operatively coupled to the pulse generator, theprocessor being programmed with instructions that, when executed:receive an input corresponding to an available voltage from the battery;identify a pulse width of an electrical signal based on a correlationbetween pulse widths and signal delivery amplitudes; and direct thepulse generator to deliver an electrical therapy signal at theidentified pulse width value using a voltage within a margin of theavailable voltage. The processor may be programmed with instructionsthat, when executed: receive at least one input corresponding to atarget current amplitude and a target pulse width; determine that theavailable voltage is insufficient to supply a therapy signal at thetarget current amplitude and the target pulse width; determine animpedance of a circuit via which the electrical therapy signal isdelivered, the circuit including the patient; based at least in part onthe impedance and the available voltage, determine an updated currentamplitude less than the target current amplitude; based on the updatedcurrent amplitude and the correlation, identify an updated pulse widthgreater than the target pulse width. The pulse generator may beprogrammed with instructions for delivering the electrical therapysignal at a frequency of from 1.5 kHz to 100 kHz (or any of theabove-described frequencies). The pulse generator may be programmed withinstructions for delivering the electrical therapy signal at a pulsewidth of from 10 microseconds to 333 microseconds (or any of theabove-described pulse widths).

While advantages associated with certain embodiments of the disclosedtechnology have been described in the context of those embodiments,other embodiments may also exhibit such advantages, and not allembodiments need necessarily exhibit such advantages to fall within thescope of the present technology. The following examples provideadditional embodiments of the present technology.

To the extent the any of the foregoing patents, published applications,and/or any other materials incorporated herein by reference conflictwith the present disclosure, the present disclosure controls.

1-69. (canceled)
 70. A method of programming a signal generator forstimulation therapy, the method comprising programming the signalgenerator to increase a signal delivery parameter of an electricalsignal in response to a decrease in an available voltage, wherein theincrease is based on a correlation between the signal delivery parameterand signal delivery amplitudes, and wherein the signal deliveryparameter is a pulse width and/or a duty cycle.